Extensive fishing of natural waters has lead to a reduction in fish numbers. It is now recognized that fishing at a rate to sustain natural populations will not provide the world's needs for fish as a food. This has lead to the development of the aquaculture industry, in which fish and other aquatic species are produced in a controlled environment within bodies of water. These fish farms can be established in ocean or fresh water depending on the type and normal environment of the fish. Fish is, worldwide, the single biggest source of protein, and aquaculture is therefore an increasingly important means of producing food. Furthermore, since the fish are in a controlled environment, means are being sought to control disease and maximize production.
Parasites, causing little apparent damage in feral fish populations, may cause diseases of great importance in farmed fish, leading to pathological changes, decrease of fitness or reduction of the market value of fish. Despite considerable progress in fish parasitology, major gaps still exist in the knowledge and control of fish parasites. Control of many important parasitic diseases are still far from satisfactory and further options are needed.
Development of aquaculture during the last decades has resulted in much greater attention being paid to problems posed by parasites and their importance to growth rate, feed efficiency and body weight leading to constraints in the advancement and productivity of aquaculture. Besides direct losses caused by mortality, parasites may have considerable impact on growth and behavior of fish, their resistance to other stressing factors, susceptibility to predation, etc.; their presence may also reduce marketability of fish.
Parasitic crustaceans are important pathogens and diseases caused by them may result in considerable economic losses. The most important group among parasitic crustaceans are undoubtedly sea lice.
Sea lice is the term used to describe several species of ectoparasitic copepods (a type of crustacean) of the genera Lepeophtheirus and Caligus that parasitize cultured fish and may cause diseases with damage to the epidermis and in severe cases death through osmoregulatory failure or secondary infections. Lepeophtheirus salmonis is now recognized as one of the most serious pathogens of marine farmed Atlantic salmon. This species and Caligus elongatus have economic impact on farmed salmonids in the northern hemisphere. Other caligids pathogenic to cultured or wild fish are C. patulus, C curtus, C. clemensi, C. rogercressey; C teres, C. orientalis, C. epidemicus and Pseudocaligus apodus. 
The most common adult copepod parasites of freshwater fishes are Lernaea cyprinacea, Ergasilus sieboldi (and related species), Salmincola californiensis, S. edwardsii, Achtheres percarum, Tracheliastes maculates, and Caligus lacustris. In addition, copepodids of Lernaea and chalimus larvae of Achtheres and Salmincola attach to gill filaments and cause epithelial hyperplasia and may be indirectly responsible for fish-kills. Copepods are also intermediate hosts for important fish parasites, including tapeworms and nematodes. Damage from these parasites may lead to fish mortalities or reduce the market value of the fish products. Finally, copepods serve as intermediate hosts for parasites that infect humans and can serve as vectors of serious human diseases like cholera.
Additional parasites of freshwater fish include monogenean trematodes (flukes or flatworms); Protozoan parasites such as Piscinoodinium pillulare; and Henneguya spp.
Formaldehyde, malathion and natural compounds show either poor efficacy or unsuitable therapeutic margins. Pyrethroids are at present the most used therapeutic against ectoparasitic copepods. Diflubenzuron and teflubenzuron added to feed are also used in significant amounts. Carbaryl and diflubenzuron are efficacious but the compounds make them unsuitable due to undesirable environmental toxicological characteristics. Emamectin benzoate belongs to the same family of drugs as ivermectin, the avermectins. It is administered in the feed and is said to be effective against all stages of sea lice reproduction. There is increasing evidence that emamectin benzoate may harm non-target animals. Despite these problems, chemotherapy remains an important component of control strategies.
The present invention provides a new technique for ectoparasitic copepod control and improved fish production.